The present invention relates to a capacitor for a DRAM cell. More particularly, the present invention relates to a stacked-capacitor for a DRAM cell having a hollow storage electrode and to a method for manufacturing the same.
Since a semiconductor memory device, particularly a dynamic RAM (hereinafter referred to as a DRAM,) is structurally reduced in the capacity of its capacitors due to high integration, it is absolutely necessary to realize a capacitor having a sufficiently large capacity even if the size of its memory cells is made small.
As a method for increasing the capacity of a DRAM cell capacitor, there have been disclosed a trench capacitor and a stacked capacitor. The trench capacitor has a trench formed on the surface of a substrate and a storage electrode formed in the inner wall of the trench and then the trench is filled with plate electrodes. The stacked capacitor has storage electrodes stacked on the substrate and the capacity of a capacitor is increased by utilizing the surface area of the extended storage electrodes.
Although the trench capacitor structure enables its capacity to increase to a considerable degree on the limited surface area, it is difficult to achieve satisfactory insulation between neighboring trenches for high integration which narrows the distance between elements. In the case of stacked capacitor structure, however, it has the advantage of increasing its capacity as compared with the trenched structure because it has enough room for extension over the substrate.
FIG. 1 illustrates an improved conventional stacked capacitor structure. On the substrate where an element separating oxide film 2, a source region 3, a drain region 4, a word line 5, a bit line 10 and an insulating film 6 are formed, the capacitor illustrated in FIG. 1 is composed of a fin-shaped storage electrode 7 which makes contact with the source region 3, a dielectric film 8 and a plate electrode 9. In the upper front of the substrate 1, an element protecting film 11 of the DRAM cell is formed.
The fin-shaped storage electrode 7 is formed by alternatively stacking and etching the polysilicon and oxide films which are arranged in several layers and then removing all of the oxide films remaining between the layers. Thereafter, the dielectric film 8 and the plate electrode 9 are formed.
In such a conventional method, however, the wing parts 71, 72 of storage electrode 7 are apt to fall apart when the substrate 1 is soaked in oxide film etching solution to remove the oxide film between layers before the dielectric film 8 is formed. In other words, the connecting parts of those wing parts 71, 72 are weakened and thereby caused to hang down or to fall apart because they become loose for lack of a supporting layer after the oxide films between layers are all removed. Consequently, this not only lowers the reliability of the process but also sets limits to a method for manufacturing capacitors stacked in several layers.